Paleogene seawater osmium isotope records

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Author(s): Rolewicz, Zach; Thomas, D. J.; Marcantonio, Franco
Author Affiliation(s): Primary:
Texas A&M University, Oceanography, College Station, TX, United States
Volume Title: AGU 2012 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2012; American Geophysical Union 2012 fall meeting, San Francisco, CA, Dec. 3-7, 2012. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Paleoceanographic reconstructions of the Late Cretaceous and early Cenozoic require enhanced geographic coverage, particularly in the Pacific, in order to better constrain meridional variations in environmental conditions. The challenge with the existing inventory of Pacific deep-sea cores is that they consist almost exclusively of pelagic clay with little existing age control. Pelagic clay sequences are useful for reconstructions of dust accumulation and water mass composition, but accurate correlation of these records to other sites requires improved age control. Recent work indicates that seawater Os isotope analyses provide useful age control for red clay sequences. The residence time of Os in seawater is relatively long compared to oceanic mixing, therefore the global seawater 187Os/188Os composition is practically homogeneous. A growing body of Late Cretaceous and Cenozoic data has constrained the evolution of the seawater Os isotopic composition and this curve is now a viable stratigraphic tool, employed in dating layers of Fe-Mn crusts (e.g., Klemm et al., 2005). Ravizza (2007) also demonstrated that the seawater Os isotopic composition can be extracted reliably from pelagic red clay sediments by analyzing the leached oxide minerals. The drawback to using seawater Os isotope stratigraphy to date Paleogene age sediments is that the compilation of existing data has some significant temporal gaps, notably between ∼38 and 55 Ma. To improve the temporal resolution of the seawater Os isotope curve, we present new data from Ocean Drilling Program (ODP) Site 865 in the equatorial Pacific. Site 865 has excellent biostratigraphic age control over the interval ∼38-55 Ma. Preliminary data indicate an increase in the seawater composition from 0.427 at 53.4 Ma to 0.499 by 43 Ma, consistent with the apparent trend in the few existing data points. We also analyzed the Os isotopic composition recorded by oxide minerals at Integrated Ocean Drilling Program (IODP) Site U1370 to construct an age model for this predominantly pelagic clay section. The 187Os/188Os values generally increase from 0.312 at 64.46 mbsf to 0.531 at 28.26 mbsf. The low value recorded at 64.46 likely reflects the Os isotope minimum recorded across the K/Pg boundary, while the uppermost value likely correlates to the E/O interval. Comparison of the Os-derived ages with a crude linearly interpolated sedimentation rate age model reveals variations in sediment accumulation rate between 0.86 and 1.5 m/Myr.
Year of Publication: 2012
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Cenozoic; East Pacific; Isotope ratios; Isotopes; Leg 143; Metals; Mid-Pacific Mountains; North Pacific; Northeast Pacific; ODP Site 865; Ocean Drilling Program; Os-187/Os-186; Osmium; Pacific Ocean; Paleo-oceanography; Paleoclimatology; Paleogene; Platinum group; Radioactive isotopes; Stable isotopes; Tertiary
Coordinates: N182624 N182626 W1793320 W1793321
Record ID: 2014077804
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